1. Field of the Invention
The present invention relates to an inflator for inflating a vehicle occupant restraint such as an air bag, and further relates to a method of assembling the inflator.
2. Description of the Prior Art
U.S. Pat. No. 4,817,828 discloses an inflator for inflating a vehicle occupant restraint such as an air bag. The inflator includes an inner tubular wall and an outer tubular wall. The inner tubular wall surrounds an ignitable gas generating material which, when ignited, rapidly produces a large volume of gas for inflating the air bag. Each of the tubular walls has a plurality of gas flow openings for directing the gas to flow radially outward from the gas generating material and through the tubular walls toward the air bag. A sheet of pressure controlling foil extends circumferentially around the inside surface of the outer tubular wall. The pressure controlling foil blocks the gas from flowing through the openings in the outer tubular wall until the pressure of the gas reaches a predetermined elevated level at which it ruptures the pressure controlling foil.
The inflator disclosed in the '828 patent further includes a cylindrical filter assembly. The filter assembly is located between the inner tubular wall and the outer tubular wall. The filter assembly has a plurality of generally cylindrical layers of filter material which remove unwanted products of combustion from the gas as the gas flows radially outward through the filter assembly. The radially outermost layer of filter material adjoins the sheet of pressure controlling foil, and is formed of coarse wire mesh screen with relatively large openings that define a plenum chamber. The gas accumulates within the inflator, including the plenum chamber, while the gas pressure is increasing toward the elevated level at which it ruptures the pressure controlling foil.
The inflator disclosed in the '828 patent is assembled by laying out flat, flexible sheets of filter material in overlying relationship with a flat, flexible sheet of wire mesh screen, and by winding the sheets around the inner tubular wall. The wound sheets then extend circumferentially around the inner tubular wall in spiral configurations, and thus define layers of the filter assembly which are generally coaxial and cylindrical. The layer of coarse wire mesh screen is then wrapped around the other layers. The filter assembly and the inner tubular wall are moved telescopically into the outer tubular wall through an open end of the outer tubular wall after the sheet of pressure controlling foil has been installed within the outer tubular wall.